New research reveals subtlety of superconductivity

Mar 20, 2007

Argonne scientists helped lead the superconducting revolution 20 years ago this month with their landmark solution of the structure of the most widely known high-temperature superconductor YBa2Cu3O7. Now, they have solved another tantalizing superconductivity mystery: how a subtle change in the structure of so-called electron-doped superconductors switches the phenomenon of superconductivity on and off.

Superconductivity is the loss of all resistance to the flow of electric current at very low temperature, a surprising phenomenon with the potential to save enormous quantities of energy if it can be applied to the electric power grid. Twenty years ago, a new class of materials that superconduct at dramatically higher temperature, up to 164 K (about 165 below zero F), was discovered, promising widespread energy-saving applications. Most of these superconductors are “hole-doped,” so named because their superconductivity is triggered by removing electrons (adding “holes”) to an insulating magnetic compound. A few of the high-temperature superconductors, however, are “electron-doped,” requiring the addition of electrons to produce superconductivity.

The mystery of these electron-doped superconductors is that in addition to electron doping, they must be heated to high temperature during their manufacture to enable them to superconduct. No one could understand why the heat treatment was necessary; it did not seem to alter the structure or composition of the material, yet it dramatically transformed the material from an insulator to a superconductor.

“Our discovery opens the door to understanding how electron-doped superconductors work,” said Stephan Rosenkranz, an Argonne scientist on the experimental team. “We didn't realize the interplay of structure and superconductivity was so subtle. But now that we know what is good for superconductivity, we can vary the amount of the good and bad stuff in systematic ways to find out what makes them tick.”

The research team lead by scientists from Argonne, the University of Tennessee, and Brigham Young University found that heating the electron-doped superconductor Pr1-xLaCexCuO4 repaired subtle flaws in the microscopic structure of the material. These flaws are so delicate that their repair by heating escaped detection for nearly two decades. The Argonne team found them by effectively looking with two magnifying glasses. They correlated measurements of copper atom positions, using X-rays at the Advanced Photon Source (APS) at Argonne, with measurements of the oxygen atom positions by neutrons at the National Institute for Standards and Technology Center for Neutron Research.

The combination of these two measurements revealed a small change in the placement of both copper and oxygen atoms taking place during the heat treatment, leading to a perfect structure and superconductivity. Furthermore, the change is fully reversible: The material could be cycled from the flawed to the perfect structure, switching the superconductivity off or on.

The X-ray experiments for this work were led by Rosenkranz and Argonne's Peter Chupas and Peter Lee. They used the high-intensity X-ray beams produced by the APS to determine the precise location and type of each atom in the crystal structure. Branton Campbell, another member of the research team and former postdoctoral researcher at Argonne, now at Brigham Young University, compared this technique to putting an object on a table, hitting it with baseballs thrown from different angles, and then using the marks left where the bounced balls struck the surrounding walls to figure out what the object looks like. Other members of the experimental team include Pengcheng Dai from the University of Tennessee and Oak Ridge National Laboratory, Hye-Jung Kang, now at the National Institute of Standards and Technology, and scientists from Tokyo's Central Research Institute of Electric Power Industry, who made the samples.

The detailed results of these findings were published in the Nature Materials paper "Microscopic Annealing Process and its Impact on Superconductivity in T'-Structure Electron-Doped Copper Oxides," which is available online. Funding for this research was provided by the U.S. Department of Energy's Office of Basic Energy Science, the U.S. National Science Foundation and the Japan Society for the Promotion of Science.

Related Stories

An interdisciplinary team of mathematicians and physicists has developed a new quantitative approach to understanding the mysterious properties of the materials called glasses. The study is described in a ...

(Phys.org) —On a quest to design an alternative to the two complex approaches currently used to produce electrons within microwave electron guns, a team of researchers from Euclid TechLabs and Argonne National ...

NIST scientists have pioneered a technology that may speed the arrival of long-awaited materials and devices including advanced high-temperature superconductors and high-efficiency photovoltaic cells: A new ...

Researchers carrying out experiments at the U.S. Department of Energy's Advanced Photon Source (APS) and Spallation Neutron Source have shed new light on how magnetic long-range order forms and remains stable ...

(Phys.org) —When is an electron hole like a quasiparticle (QP)? More specifically, what happens when a single electron hole is doped into a two-dimensional quantum antiferromagnet? Quasiparticle phenomena ...

(Phys.org) —Like the perfect sandwich, a perfectly engineered thin film for electronics requires not only the right ingredients, but also just the right thickness of each ingredient in the desired order, ...

Recommended for you

Researchers at the University of Houston have created a new thermoelectric material, intended to generate electric power from waste heat - from a vehicle tailpipe, for example, or an industrial smokestack ...

Magnetic vortex structures, so-called skyrmions, could in future store and process information very efficiently. They could also be the basis for high-frequency components. For the first time, a team of physicists ...

For almost a century, scientists have been puzzled by a process that is crucial to much of the life in Earth's oceans: Why does calcium carbonate, the tough material of seashells and corals, sometimes take ...

If you put a camera in the ice machine and watched water turn into ice, the process would look simple. But the mechanism behind liquids turning to solids is actually quite complex, and understanding it better ...

Wake up in the morning and stretch; your midsection narrows. Pull on a piece of plastic at separate ends; it becomes thinner. So does a rubber band. One might assume that when a force is applied along an ...

User comments : 0

Please sign in to add a comment.
Registration is free, and takes less than a minute.
Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.

Javascript is currently disabled in your web browser. For full site functionality, it is necessary to enable Javascript.
In order to enable it, please see these instructions.